In the assembly of automotive wheels and tires, a tire is mounted onto a wheel and then inflated. Prior to mounting the tire, a valve stem must be inserted into a valve stem opening in the wheel to permit inflation of the tire. For manufacturing wheels on a large production scale, machines are used to automatically insert the valve stems into the wheels. Because wheels of different sizes require different sized valve stems, valve stemming machines must either operate on wheels of a single size or be able to accommodate the use of several sizes of valve stems. For example, some prior art devices utilize a rotatable carousel to dispense valve stems of varying sizes onto a valve stem insertion tool.
Other prior art devices include mechanisms for detecting the wheel size and providing the appropriate valve stem based upon the wheel size. For example, U.S. Pat. No. 4,353,156 to Rosaz discloses a valve stemming machine that accommodates different wheel sizes by relying on the consistency among different sized wheels of (1) the angle between the wheels rotational axis and the normal to the valve bearing face and (2) the distance from the center of the valve hole to the wheel's edge, measured in the valve bearing plane. By inserting valve stems based upon these two geometric features, different sized wheels can be accommodated without knowing further information about the wheels.
Valve stemming machines generally rotate the wheel and detect when the valve stem opening is aligned with a valve stem insertion tool. Unfortunately, prior art machines for detecting the position of the valve stem opening are generally imprecise. In the Rosaz '156 reference, the machine includes both a valve hole detection station and an insertion station at different locations about the circular path through which the rim of the wheel is rotated. The wheel is rotated while light at the detection station shines upwardly at the wheel. When the valve hole reaches the detection station, light passes through the valve hole and strikes a detection cell. Rotation is continued at a slower speed using a drive roller that is rotated through a fixed angle to align the valve hole with the insertion station. As will be appreciated, alignment between the valve hole and the insertion station is not actually detected or confirmed, but is assumed based upon the fixed angular rotation. Consequently, slippage between the drive roller and wheel, differences in diameters of the wheels, and other such factors can adversely affect the accuracy of the final positioning of the valve hole at the insertion station. Also, depending upon the sensitivity of the detection cell and the intensity of outside light, the precise position at which the valve stem opening is detected can vary significantly.
Some prior art devices which utilize a photodetection cell similar to the Rosaz '156 reference will rotate the wheel at high speed until the valve stem opening is first detected, stop the wheel, and then reverse the rotation of the wheel at slow speed until the valve stem opening is detected again. However, this method still does not significantly improve the accuracy of detecting a valve stem opening with a photodetection cell.
If the valve stem opening is not precisely aligned with the valve stem insertion tool, relative adjustment between the valve stem insertion tool and the wheel can be required. In the Rosaz '156 reference, a recentering spindle is utilized to center the valve stem opening with the valve stem insertion tool. The requirement for a separate device to center the valve stem opening increases the cost and complexity of the machine, and the prior art does not provide for a valve stem insertion tool which is universally adjustable to avoid the need for extraneous centering devices.